The existence of an acetylcholine (ACh)-choline acetyltransferase (ChA)-acetylcholinesterase (AChE) system in the human placental trophoblast has been demonstrated by our investigations. Since the placentae lack innervation, and ACh does not exhibit a significant effect on the placental vascular system, ACh is possibly involved in the transport of charged molecules across the trophoblast, and ACh release and stimulation of a cholinergic receptor is intimately coupled to the transport process ("stimulation-transport coupling"). If this hypothesis is true, placental cholinergic system has a significant role on the growth and development of the fetus. Therefore, we have undertaken this investigation with the following specific objectives: (1) Relationships between cholinergic nervous system, pregnancy and fetal growth. (2) Characterization of human placental cholinergic receptor. (3) Influence of cholinomimetics, AChE-inhibitors, ChA-inhibitors, and drugs which exhibit AchE-inhibition as a side effect (e.g., morphine, LSD-25) on the transport of ions (Na ions, K ions, Ca ions), amino acids, sugars and proteins across the trophoblast. (4) Mechanisms of release of placental ACh and the role of Ca ions, prostaglandins and cyclic AMP in ACh release. (5) Influence of placental cholinergic on the drug transport (aspirin diuretics of sulfonamide type, barbiturates and antihistamines). (6) Role of ACh on the release of chorianic gonadotrophin and progesterone from the human placenta. These investigations will lead to the understanding of the role of ACh in transport of material across the placental trophoblast, the nature of the placental barrier, and their relationships to the fetal development.